The patent application relates to a device for cutting external threads in the peripheral outer surface of an elongated cylindrical work, such as a pipe, rod etc. and more particularly to a screw cutter die head.
There are various methods or means for cutting screw threads on such work, such as lathe, die, die head, thread milling and thread grinding, each of which has respective advantages and disadvantages.
The method using a die having cutting edges on an inner peripheral wall thereof is advantageously simple in construction but disadvantageous particularly in that when a desired length of thread has been formed along the extended work the die must be rotated in the other direction to remove the die from the work, and in that the central opening thereof for the work to pass through is not variable, so that the tool must be changed each time depending on the varied outer diameter of the work.
Different therefrom, the so-called die head which generally has four or five chasers circumferentially mounted thereon to be radially movable in the central opening towards the circle center or in the other direction, allows the work to be removed therefrom without necessity of reverse rotation, because the chasers may be simultaneously retracted in the respective radial directions when the necessary screw cutting is over.
The die head generally comprises an annular body portion holding said chasers to be radially movable, an annular support member fixed thereto and a ring member having a corresponding number of circle arc cam ridges formed on one side surface thereof and adapted to be angularly movable between and relative to said annular body portion and annular support member, all of which have a central opening for the elongated cylindrical work to pass therethrough to be formed with external threads by multiple cutting edges formed at the inner ends of said chasers.
Each of said chasers has a recess to ride on each of said cam ridges extended to be in a circle arc and arranged to be inclined with respect to a circumference passing through a center point in the length thereof so that when the ring member is angularly moved relative to the assembly of said annular body portion and said annular support member in either direction, each of said chasers may respectively slide along each of the slantedly arranged cam ridges to be radially moved in the corresponding direction to be in the position where the cutting edges of each of the chasers may engage with the peripheral surface of the work for screw cutting or in the other or retracted position where the chasers are no longer engaged with the work so as to allow said work to be freely removed from the die head.
As well known to those skilled in the art, the elongated cylindrical work such as pipes and rods to be formed with external thread have respective diameters stepwisedly varied, i.e. increased or decreased in such a manner as predetermined by the govermental standard or manufacturers' agreement, according to which said angularly movable ring is rotated, and then fixed so as not to be angularly moved more, generally by fitting a latch held on the annular body portion of the die head in any corresponding one of a plurality of notches or recesses formed in said rotatable ring member around the outer peripheral wall in pitches corresponding to those of the stepwisedly varied diameter of the work so that the inner ends of the chasers may proceed with necessary screw cutting of the work having the corresponding outer diameter. Then, a chuck holding the elongated cylindrical work for rotation and the die head is relatively moved together in the axial direction so as to actually proceed with screw cutting. The die head, thus, may cope with the works having various diameters in a range to be decided by the number of the notches or recesses to be engaged with the latch and the inclination angle of the cam ridge to be engaged with the cam recess formed in the chaser.
The die head is generally formed with a pivoted detector so that when the external thread is cut along a predetermined length of the work, the free end of the elongated work may abut thereon to cause mechanical action for automatically disengaging said fixation of the angularly movable ring from the die head so as to allow release of the work.
The die head of the art referred to above is already in public knowledge e.g. from Japanese Official Gazette Sho No. 57 (1982)-20101 of Apr. 26, 1982 for opening the examined Patent Application filed by Asada Kabushiki Kaisha designated as the assignee of the present patent application to be laid open to public inspection.
There is, however, a limit to the range of varied diameters of the work with which the die head of the type referred to above can cope. The number of the notches to be formed around the angularly movable ring is to be limited in an arc angle corresponding to that of the arc cam ridge, because even if the notch number is increased and consequently even if the arc angle along which the notches are formed is increased, the chase is to be disengaged from the cam ridge so as not to radially move. It is obviously difficult to make the arc cam ridge to be slanted so sharply. In order to proceed with screw cutting on further larger or smaller diameter of the work, thus, the chasers must be exchanged with new ones in each of which the cam recess is formed at a location nearer to the inner end or the outer end thereof.
Thus, one object of the invention is to provide a die head capable of coping with a wider range of varied diameters of the elongated cylindrical work to be formed with external thread without necessity of changing the chasers each time.
The object referred to above can be attained by using the chaser formed with a plurality of cam recesses and forming the corresponding number of groups of the notches or recesses to engage with the latch for fixing the angularly movable ring member relative to the die head.
The invention will be explained in more detail with respect to a preferred embodiment with reference to the accompanying drawings.